The present invention relates to the field of photography, and more particularly to flash photography using electronic flash units which can provide different cones of light output when using a zoom lens or lenses of different focal lengths.
In recent years, electronic flash units have been provided with zoom heads which allow the angle of the cone of light produced by the flashtube of the flash unit to be selected for use with different focal length lenses. Examples are the Vivitar 285, 2500 and 3500. Each of these includes a sliding or extendible head with a Fresnel lens in front of the flashtube. The head may be moved in and out, and thus toward and away from the flashtube, to adjust the angle of the cone of light emitted by the flash unit. In a typical electronic flash unit of this nature, one position is for wide angle photography, another is for normal photography, and another is for telephoto photography.
When flash units of this nature are used, it is necessary for the photographer to select the appropriate position for the zoom head of the flash unit to correspond to the focal length of the lens being used on the associated camera or to correspond to the focal length selected on a zoom lens being used. While this is a relatively simple operation, photographers sometimes forget to make this change in the zoom head, and in any event the need to make any such adjustment intereferes with composing and shooting a picture.